54 



R. BOTTGER-SCHNACK 



Oncaea media Giesbrecht, 1891 



Oncaea media Giesbrecht (1891): 477. 



Oncaa media Giesbrecht (1892) 



Reliable descriptions. Giesbrecht (1892): 591-600, 602, 603, 

 756, 757, 774, Plate 47, Fig. 1 (not Fig. 11), 29-33, 40 [as Oncaa 

 media]; Tanaka (1960): 69,70, Plate XXXI, Figs. 4-9; Heron & 

 Bradford-Grieve (1995): 36, 39, Figs. 15k, 16a-k, 17a-i, 26b; Itoh 

 [in: Chihara & Murano 1997]: 980, Fig. 365a-f. 



Doubtful descriptions. Dakin & Colefax (1940): 117, Fig. 

 205C a [9only]; Chen et al. (1974): 41-42, Plate 6, Figs. 12-15; 

 Mori (1937; reprinted 1964): 120-121, Plate 66, Figs. 14-18. 



Type LOCALITY, not specified; original description based on 

 material from various locations near the equator in the tropical 

 Pacific. 



Preliminary note. Giesbrecht's original material of O. media 

 was not available for study, because it is not allowed to be sent out 

 on loan (A. Ianora, Zoological Station Naples, pers. comm.). Heron 

 & Bradford-Grieve (1995) gave an excellent redescription of O. 

 media based on specimens from the Gulf of Naples and provided a 

 summary of its distribution in the Pacific Ocean and other areas. 

 They pointed to the great similarity between O. media and O. 

 scottodicarloi, which they described as a new species, and cleared 

 up the confusion in Giesbrecht's ( 1 892) redescription with regard to 

 these two species. Specimens from the Red Sea agreed in almost 

 every detail with the redescription of Heron & Bradford-Grieve 

 (1995). However, some morphological characters are described 

 below, which were not noted by Heron & Bradford-Grieve and/or 

 appeared to differ between the two areas. Also, the body dimensions 

 of the species from the Red Sea calculated by the different methods 

 used throughout this study are provided. 



Material examined. 



( 1 ) Northern Red Sea, 22° 58.4'N, 37° 19.4'E: Stn. 663; WV Meteor 

 leg 5/5 : collected 20 July 1 987 with MSN 0.05 mm net (Haul 1 II 

 4); depth 50-100 m; total water depth ca 1200 m. 



(a) 2 99 in alcohol (BMNH 1998.2797-2798). 



(b) 1 6 in alcohol (ZMH K-39584). 



(c) 1 9 dissected on slides, 2 99 in alcohol; 1 8 dissected on 

 slides, 2 88 in alcohol (RBS). 



(2) Gulf of Aden, 11° 55.5'N, 43° 37.9'E: Stn. 631; R/V Meteor leg 

 5/5: collected 1 1 July 1987 with MSN 0.05 mm net (Haul 3/5); 

 depth 0-50 m; total water depth ca 1400 m. 



(a) 2 99, 2 c^d in alcohol (BMNH 1998.2799-2802). 



(b) 2 99, 2 88 in alcohol (ZMH K-39585). 



(c) 2 99(1 ovigerous), 2 88 in alcohol, (RBS). 



Description. Note illustrations are based on 1 (c). 



Adult female (Fig. 15). 



Body length: 884 urn [traditional method: 710 urn, range: 650-770 



urn, based on 22 specimens (Bottger-Schnack et al., 1989)]. 



Exoskeleton moderately chitinized. Prosome 2.6 times length of 

 urosome, excluding caudal rami, 2.2 times urosome length includ- 

 ing caudal rami. P2-bearing somite without conspicuous 

 dorso-posterior projection visible in lateral aspect (Fig. 15B). 

 Integumental pores on prosome as indicated in Fig. 15 A, B. Pleural 

 areas of P4-bearing somite with rounded posterolateral corners. 



Proportional lengths (%) of urosomites 13.0 : 62.7 : 8.5 : 6.1 : 9.7. 

 Proportional lengths (%) of urosomites and caudal rami 1 1.4 : 55.2 

 : 7.5: 5.3: 8.5 : 12.1. 



Genital double-somite 1.9 times as long as maximum width 



(measured in dorsal aspect) and 2.6 times as long as postgenital 

 somites combined (Fig. 15C). Genital apertures with armature 

 represented by 1 spine and 2 minute spinous processes (Fig. 151) 

 [the latter 2 not mentioned by Heron & Bradford-Grieve]. Double- 

 curved sclerotization between genital apertures, pore pattern on 

 dorsal surface as indicated in Fig. 15C. 



Anal somite 2.0 times wider than long: about 2/3 length of caudal 

 rami (Fig. 15C). Ornamentation as in O. venusta. 



Antennule with armature as for genus, small element on 6th 

 segment (arrowed in Fig. 15 D) not mentioned by Heron & Brad- 

 ford-Grieve. 



Antenna as figured by Heron & Bradford-Grieve (their Fig. 16c), 

 except for seta I of lateral armature on first endopod segment slightly 

 longer than figured by these authors; additional surface ornamenta- 

 tion on coxobasis as in O. waldemari (cf. Fig. 25A). 



Labrum (Fig. 15E, F) as for O. venusta, but lacking patch of 

 setules on posterior face at posterior part of each lobe. [O. media is 

 the only species of Oncaea s.str. that misses these setules.] 



Mandible mainly as figured by Heron & Bradford-Grieve (their 

 Fig. 16e), except for dorsal blade (C) ornamented with 4 dentiform 

 processes at distal margin. 1 of them inserted subdistally, and 1 

 minute process halfway at dorsal margin (Fig. 16E). Maxillule, 

 maxilla and maxilliped mainly as figured by Heron & Bradford- 

 Grieve (their Figs. 16f-h), but with additional surface ornamentations 

 and microstructures, such as 2 large secretory pores (not 1 ) on 

 surface of maxilla and third single row of shorter spinules along 

 outer margin of strong maxillary spine (similar to O. waldemari, cf. 

 Fig. 25F). [Complete pattern of microstructures on surface of ex- 

 oskeleton not additionally figured in present account, but generally 

 similar to those observed for O. venusta and O. waldemari]. 



Swimming legs with armature as for genus and surface ornamenta- 

 tion similar to O. waldemari (cf. Figs. 26A-D). P1-P4 with spines on 

 exp-1 longer than figured by Heron & Bradford-Grieve (their Figs. 

 16i-k, 17a), reaching beyond half length of spine on exp-2. PI with 

 inner basal element minutely pinnate (Fig. 1 5G), not naked as figured 

 by Heron & Bradford-Grieve; distal margin of exp- 1 and -2 ornamented 

 with long spinules anteriorly as in O. scottodicarloi (cf. Fig. 23C). 



P5 (Fig. 1 5H) with exopod longer than wide, length to width ratio 

 1.7: 1. 



P6 (Fig. 151) armed with a spine and 2 small spinous processes 

 [the latter 2 not mentioned by Heron & Bradford-Grieve]. 



Adult male (Fig. 16). 



Body length: 672 urn [traditional method: 560 urn, 1 specimen]. 

 Sexual dimorphism in antennule, antennary setae, maxilliped, PI- 

 PS (endopod) and P5-P6, caudal ramus and in genital segmentation. 



Prosome 2.2 times the length of urosome, excluding caudal rami, 

 1.9 times urosome length, including caudal rami. 



Proportional lengths (%) of urosomites (excluding caudal rami) 

 12.3 : 66.4 : 4.3 : 3.7 : 4.3 : 8.6; proportional lengths (%) of 

 urosomites (caudal rami included) 10.9 : 58.7 : 3.8 : 3.3 : 3.8 : 7.6 : 

 11.9. Caudal rami about as long as wide, much shorter than in 

 female. Caudal setae with proportional lengths as in female, except 

 for seta VI, which is about 2/3 the length of seta IV and 3 times the 

 length of caudal ramus (Fig. 16A). 



Antennule with armature as for genus. 



Antenna (Fig. 16D) as in female, except for seta on coxobasis 

 naked and shorter than in female [not mentioned by Heron & 

 Bradford-Grieve]; lateral armature on distal endopod segment dif- 

 fering from female, with spiniform seta III much stouter and seta IV 

 spiniform and curved, with row of dentiform processes along outer 

 distal margin; both elements shorter than in female. 



